1. Field of the Invention
The present invention generally relates to a sheet thickness detecting device detecting the thickness of a sheet passing through a conveying path, a feeding device including the sheet thickness detecting device, and an image forming apparatus such as a copier, a printer, a facsimile machine, a multi-functional peripheral including thereof and the sheet thickness detecting device.
2. Description of the Related Art
To detect a thickness of a sheet passing through a conveying path in an image forming apparatus including a copier, a printer and the like, there has been known a technique using a detecting unit that detects the thickness (sheet thickness) of a sheet (e.g., a sheet material, a recording medium) fed on the conveying path, so as to vary an image forming condition and a feeding condition based on the detection result (see for example in Patent Documents 1 and 2).
Patent Document 1: Japanese Laid-open Patent Publication No. 2004-252233
Patent Document 2: Japanese Patent No. 4152136
Specifically, to detect the sheet thickness, a feeding roller pair including a fixed roller and a movable roller is provided in a conveying path to an image forming part and on the upstream side of the image forming part, so as to detect the displacement amount of the moving roller moving in accordance with the thickness of a sheet by using a detecting unit (sheet thickness detecting unit) while the sheet is sandwiched and fed by the feeding roller pair.
By using an image forming apparatus including such a detecting mechanism, it is no longer necessary for an operator to input data indicating the sheet thickness whenever the operator sets a sheet in the apparatus main body. Therefore, such an image forming apparatus may be an easy-to-use apparatus.
On the other hand, in Patent Document 2 and the like, a technique is disclosed that is aimed to accurately measure the sheet thickness by contacting one end of a lever rotating around a shaft with respect to a moving roller and by detecting the displacement amount of the other end of the lever using a sensor so as to indirectly detect the sheet thickness.